1. Field of Invention
This invention relates in general to an image forming apparatus capable of detecting an amount of powder on a surface of a powder electrostatic transferring device.
2. Discussion of the Background
An image forming apparatus, such as a copy machine, a facsimile, or a printer, etc., mentioned in Japanese Laid Open publication No. 2004-279829 and Japanese Laid Open publication No. 2004-139038, is known. In such an image forming apparatus, a latent image is formed on a latent image bearing member. Powder toner is adhered onto the latent image, and then the latent image is developed as a toner image. The toner image is transferred onto a recording medium, or onto an intermediate transfer medium and then onto a recording medium. In this way, an image is formed. In such an image forming apparatus, there is a developing device for developing the latent image. Conventionally, toner stirred within the developing device is transferred to a surface of a developing roller used as a developer bearing member, the toner is carried to a position facing the surface of the latent image bearing member, and the latent image on the latent image bearing member is developed by the toner. After the development is finished, toner not transferred to the latent image bearing member is recovered back to the developing device by the rotation of the developing roller, so that the toner is stirred and charged, and transferred to the developing roller again.
In this arrangement, the toner is sometimes rubbed between the developer bearing member and the latent image bearing member as the toners are moving on their surfaces, and is firmly fixed to one of the surfaces, adversely affecting the image. In addition, the toner is supposed to be moved electrostatically in the developing region by the electrical potential difference between the surface of the developer bearing member and the electrostatic latent image on the latent image bearing member, but this electrical difference must be fairly large. This is because a force, which is sufficient to overcome the adhesive force of the toner to the developer bearing member that results from van der Waals forces, image forces, or the like, must be imparted to the toner prior to the start of electrostatic movement for overcoming adherence to the developer bearing member. This requires a large electrostatic force.
On the other hand, it is known that in an image forming apparatus, as disclosed in Japanese Laid Open Publication No. 2004-170796, development of a latent image on a latent image bearing member is performed without a developer bearing member whose surface is moving. A development device in such an image forming apparatus has a toner electrostatic transporting substrate around which is arranged a plurality of transporting electrodes at intervals as a transporting electrodes loading device. In this arrangement, transportation of toner to the developing region using a toner electrostatic transporting substrate enables development with lower electric potential than using a developer bearing member whose surface is moving.
In addition, a developing apparatus requires a stable supply of toner for obtaining a stable image density.
Above mentioned Japanese Laid Open Publication 2004-279829 discloses development using a developer bearing member whose surface is moving, such as a developing roller or the like. In this document, to supply a stable amount of toner to a developing region, a pattern image is formed in non-image portion on a photo conductor, the density of the pattern image is detected, and the amount of toner supplied to the developing roller is adjusted based on the result of the detection.
On the other hand, in above mentioned Japanese Laid Open Publication 2004-139038, which discloses development using a toner electrostatic transporting substrate, to supply a stable amount of toner to a developing region, a pattern image is formed in a non-image portion on a photo conductor, the density of the pattern image is detected, and the amount of toner supplied to the toner electrostatic transporting substrate is adjusted based on the result of the detection also.
However, when an amount of toner is supplied to the developing region, there is a following drawback with the above method in which a pattern image is formed on a photo conductor for the detection. In fact, the amount of toner adherence is affected by an electrostatic characteristic of a photo conductor, conditions of charge and exposure, etc., not only by an amount of toner transported to the developing region. Consequently, for adjusting an amount of toner supplied to toner electrostatic transporting substrate, it is desirable that the amount of toner is supplied to the developing region. Further, not limited to case of transporting toner, such as a toner electrostatic transporting substrate, the ability to detect the amount of the transporting toner is desirable for a fine particle electrostatic transporting device which transports a fine particle by causing relative movement on the surface thereof.